High pressure electric discharge lamp having an auxiliary starting device affixed to at least one electrode



Jan. 9, 1968 A. w. OLSON ETAL 3,363,132

HIGH PRESSURE ELECTRIC DISCHARGE LAMP HAVING AN AUXILIARY STARTING DEVICE AFFIXED TO AT LEAST ONE ELECTRODE Filed Dec. 50, 1965 ALBERT W. OLSON CARL L. PETERSON INVENTORS l/ ATTOR EY United States Patent 3,363,132 HIGH PRESSURE ELECTRIC DISCHARGE LAMP HAVING AN AUXILIARY STARTING DEVICE AFFIXED TO AT LEAST ONE ELECTRODE Albert W. Olson, Rockport, and Carl L. Peterson,

Gloucester, Mass, assignors to Sylvania Electric Products Inc., a corporation of Deiaware Filed Dec. 30, 1965, Ser. No. 517,688 6 Claims. (Cl. 313-198) This invention relates to high pressure electric discharge devices and particularly to those which contain a fill including a halogen and a metal other than mercury alone, so that the light emitted is different than the characteristic mercury emission. Specifically this invention relates to a means to reduce the starting voltages of such devices.

characteristically, lamps which contain ingredients other than mercury alone, have starting voltages which are higher than mercury lamps. If these lamps of multiple element fills are to be installed in existing sockets, they must have starting voltages which are compatible with existing ballasts.

We have now discovered that the starting voltages can be decreased materially by placing an extension on the electrode so that an arc glow can form easily between a starting probe which is placed along side of it. The are glow will cause the mercury in the arc to vaporize and an arc will then shift to between the electrode itself and the starting probe. When sufliciently warm, the arc will transfer to between the electrodes and the primary light emitting arc will form.

Accordingly, the primary object of our invention is lowering the starting voltages of the lamps which contain metals other than mercury alone in the arc tube.

The many other objects, features and advantages of our invention will become manifest to those conversant with the art upon reading the following specification when taken in conjunction with the accompanying drawings wherein the preferred embodiments are shown and described by way of illustrative examples.

Of the drawings, the figure is an elevational view of an arc tube, partially broken away to expose the inside.

Referring now to the drawing, the arc tube is generally made of quartz, although other types of glass may be used such as alumina glass or Vycor, the latter being a glass of substantially pure silica. Sealed in the are tube 12, at the opposite ends thereof are main discharge electrodes 13 and 14 which are supported on lead-in wires 4 and 5 respectively. Each main electrode comprises a core portion which may be a prolongation of the lead-in wires 4 and 5 and may be prepared of a suitable metal such as for example molybdenum or tungsten. The prolongations of these lead-in wires 4 and 5 can be surrounded by molybdenum or tungsten wires helixes. If desired, a small sliver of a metal or low work function such as thorium, which in this case should be less than about 0.5 mg., can be disposed between the helix and the rod in each of the electrodes to reduce cathode drop. In some cases when its spectrum is not desired, or limitation of the spectrum is preferred thoriated tungsten wire (containing about 2 to 4% thorium by weight) can be used or, of course, the thorium can be eliminated entirely.

An auxiliary starting probe or electrode 18, generally prepared of tantalum or tungsten is provided at the base end of the arc tube 12 adjacent the main electrode 14 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described have their ends welded to intermediate foil sections 8, 9, and of molybdenum which are hermetically sealed within the pinched sealed portions of the are tube. The foil sections are very thin, for example, approximately 0.0008 inch thick and go into tension without rupturing or sealing off when the heated arc tube cools. Relatively short molybdenum wires 23, 24 and 35 are welded to the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 12. The pinched or flattened end portions of the arc tube 12 form a seal which can be of any desired width and can be made by flattening or compressing the ends of the arc tube 12 while they are heated.

The are tube 12 is provided with a filling of mercury which reaches pressures in the order of one half to several atmospheres during normal lamp operation at temperatures of 450 to 700 C. Moreover, the fill contains a halogen, particularly iodine and except fluorine, added as the halogen per se or a halide of one of the metals in the arc tube. As the source of emission other than mercury, we add a light emitting metal as will be described later and as noted above, the alkali metal, particularly sodium, is used to control the operating voltage of the arc and its characteristics. The amount of mercury added can be varied widely as we have indicated but we prefer to add approximately 2.5 10 to 4.1 10- gram atoms of mercury per centimeter of arc length. However, substantial light emission can be obtained at filling pressures less than the above stated limits. Furthermore, the light emission appears to be substantially independent of the amount of mercury metal added and hence the quantity of the latter can be reduced while lamp operation is still attained. As is conventional in the art, a quantity of rare gas such as helium, argon, neon, krypton or Xenon at a pressure of about 25 millimeters of mercury is added to facilitate start ing.

In manufacturing arc tubes of lamps containing fills other than mercury alone, many metals can be included such as cadmium, gallium, indium, molybdenum, certain rare earth metals, scandium, thallium, thorium and vanadium. Moreover, each of these lamps should contain an alkali metal, preferably sodium for the reasons described above.

The starting extension 30 of this invention is disposed on the rod 4 and extends towards the probe 18. It may be placed on either side of the coil 14. Preferably, it spans about 5 to s of the distance between the starting probe 18 and the rod 4. It is preferably 10% to 60% of the thickness of the rod 4 and is made of the same metal. If desired, however, it may be formed by narrowing down and extending to a similar degree the coil 14 upon the rod 4. When a potential is impressed between the starting probe 18 and the rod 4, an arc will form between the starting probe 18 and the starting extension 30. The are then travels to the rod 4 and eventually will transfer to between the two electrodes.

The benefits of the starting extension are shown by the following table:

TABLE I Starting Voltage Hours Control Lamp A Lamp B Lamp 0 Hence it is clear that when the lamp has aged, the starting voltages are about 10 to 40 volts less than the control. It is apparent that modifications and changes may be made within the spirit and scope of the instant invention,

3 but it is our intention, however, only to be limited by the spirit and scope of the appended claims.

We claim:

1. A high pressure electric discharge device comprising: a quartz glass are tube; a press seal disposed at either end thereof; a rod of tungsten forming an electrode extending from each of said press seals; a starting probe disposed adjacent said rod of tungsten and extending from at least one of said press seals; means to conduct current to each of said electrodes and said starting probe; means disposed upon at least one of said electrodes and extending therefrom to facilitate starting.

2. The device according to claim 1 wherein a starting probe is disposed adjacent said electrode and said means extends from said electrode to near said starting probe.

3. The device according to claim 1 wherein the fill includes mercury, a halogen and a light emitting metal.

4. The device according to claim 3 wherein said starting extension, extends between to s of the gap between said electrode and said probe.

5. The device according to claim 3 wherein said starting extension has a diameter of to 60% of the electrode.

6. A high pressure electric discharge device comprising: a quartz glass are tube having a fill including mercury, a halogen and a light emitting metal; a press seal disposed at either end thereof; a rod of tungsten forming an electrode extending from each of said press seals; a starting probe disposed adjacent said rod of tungsten and extending from at least one of said press seals; lead-in Wires connected to each of said electrodes and said starting probe; an extension disposed upon at least one of said electrodes to facilitate starting; said extension having a' diameter of 10 to of said one of said electrodes and extending towards said probe between 20 and of the gap therebetween.

References Cited UNITED STATES PATENTS S. D. SCHLOSSER, Primary Examiner. JAMES W. LAWRENCE, Examiner. 

1. A HIGH PRESSURE ELECTRIC DISCHARGE DEVICE COMPRISING: A QUARTZ GLASS ARC TUBE; A PRESS SEAL DISPOSED AT EITHER END THEREOF; A ROD OF TUNGSTEN FORMING AN ELECTRODE EXTENDING FROM EACH OF SAID PRESS SEALS; A STARTING PROBE DISPOSED ADJACENT SAID ROD OF TUNGSTEN AND EXTENDING FROM AT LEAST ONE OF SAID PRESS SEALS; MEANS TO CONDUCT CURRENT TO EACH OF SAID ELECTRODES AND SAID STARTING PROBE; MEANS DISPOSED UPON AT LEAST ONE OF SAID ELECTRODES AND EXTENDING THEREFROM TO FACILITATE STARTING. 